This invention relates to thrust augmenters, and more particularly to rotary jet ejectors incorporating a core flow arrangement.
U.S. Pat. No. 3,046,732 to Foa, incorporated herein by reference, discloses a method and apparatus for effecting a highly efficient direct energy transfer between a primary or driving fluid and a secondary fluid. One arrangement set forth, the axial flow rotary jet, contemplates a rotor carrying nozzles oriented so that they are skewed relative to the axis of the rotor and communicating with a source of primary fluid under pressure. The region occupied by the driving fluid emerging from the rotor rotates about the same axis and at the same angular velocity as the rotor. The boundaries of this region are interfaces separating the driving fluid from the driven fluid with the relation of the interfaces to the induced flow pattern dynamically substantially like that of blade or vane surfaces of the same shape rotating at the same angular velocity. Thus the driving fluid forms "pseudo-blades", the action of which on the driven fluid is somewhat similar to the flow induction process of solid vanes or blades in dynamic flow machines. Where the stream issuing from the rotating orifice has an axial component such that its axis in its rotation describes a hyperboloid which is nearly a cylindrical surface, and the interaction space is shrouded, substantial thrust augmentation is typically produced by the resultant induced secondary fluid flow.
One of the main obstacles to the attainment of the maximum potential performance of axial-flow, rotary jet energy exchange mechanisms, of the kind disclosed in U.S. Pat. No. 3,046,732, has been found to be the occurrence of fluid flow separation over the trailing surface of the rotor casing (also known as the afterbody) where the pressure increases in the direction of the flow of fluid. Flow separation results in not only an increase of the pressure drag, but also a recirculation of flow of secondary fluid induced by the primary jet flow. This latter result is particularly undesirable inasmuch as it produces a loss of pumping effectiveness of the "pseudo-blades". Well known methods exist for retarding or preventing flow separation in regions of adverse pressure gradient, e.g., boundary layer suction or injection, "vortex generators", and others, but all such methods entail either flow losses or mechanical complications, or both.